1. Field of the Invention
The present invention relates to compressor start-up controllers to control the start-up of a compressor whose interior is filled with a liquid refrigerant.
2. Description of the Related Art
Generally, in the freezing cycle, when a compressor is suspended for a long time or the temperature of a compressor at the start-up is lower than ambient temperature (for example, that of the heat exchanger), the refrigerant is condensed within the compressor, and the gaseous refrigerant is liquefied to fill the compressor interior together with the lubricating oil, resulting in the so-called asleep state. If the compressor is started in this state, the liquefied refrigerant and the lubricating oil within the compressor are liquid-compressed so that the pressure within the compressor is unusually increased. As a result, the bearing of the compressor is damaged or seized, resulting in breakage. If the asleep refrigerant is in a large quantity, even the start-up is impossible.
To prevent the above problems, the following countermeasures have been proposed.
(1) A heater is disposed in the compressor crankcase. The heater is turned on before starting up to evaporate the liquefied refrigerant in the compressor (Japanese UM patent application Kokai No. 3-99,886).
(2) Before starting up, the compressor is rotated reversely to remove the liquefied refrigerant in the compressor from the inlet port (Japanese patent application Kokai No. 3-149,390).
(3) At the start-up, the compressor is driven at a very slow rotation to discharge the liquefied refrigerant from the outlet port so as to operate the compressor as a liquid pump (Japanese patent application No. 3-218,748).
However, the above countermeasure (1) has the following disadvantages: the number of parts is increased, the compressor size is increased, the liquefied refrigerant cannot be removed completely, and the start-up cannot be made instantly.
The above countermeasure (2) has such a disadvantage that the interior liquefied refrigerant cannot be surely flown for removal by the reverse rotation of the compressor.
The above countermeasure (3) suffers from such a drawback that when the compressor is driven at a very slow speed, the angular velocity is increased due to a backlash of the bearing and a residual gas in the compressor at the commutation of a brushless DC motor, causing the compressor to vibrate.
In addition, the rate of change of exciting current waveform passed to two of the windings of each phase becomes very sharp as shown in FIG. 9, and the vibration of the compressor becomes large due to the backlash and residual gas as shown in FIG. 9.